The purpose of the project is to study the effect of perinatal endocrinopathies on enzymes from biochemical pathways critical to the incorporation of pyrimidines into nucleic acids during rat cerebellar development. The endocrinopathies include perinatal hyperthyroidism, hypothyroidism, and hyperglucocorticoidism. Enzymes to be studied are thymidine kinase, uridine kinase, and aspartate transcarbamylase. Parallel studies will include the developmental cerebellar histopathology in these endocrinopathies, as well as study of the interrelationships between pituitary, thyroid, and adrenal hormones in such endocrinopathies during early development of the rat. Hormones studied will include corticosterone, thyroid stimulating hormone, and rat growth hormone. Additionally, these endocrine relationships in undernutrition will be studied where appropriate, in relation to the above mentioned endocrinopathies.